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Data from: Development of sound localization strategies in children with bilateral cochlear implants

Zheng Y, Godar SP, Litovsky RY

Date Published: August 25, 2015

DOI: http://dx.doi.org/10.5061/dryad.0m09h

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Title

Stimulus WAVE Files used in localization task

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Description

Stimuli consisted of bi-syllabic Children’s Spondees that have been previously used for studies on spatial unmasking of speech in children with NH [14], and with BiCIs[15], recorded with a male voice at a sampling rate of 44 kHz. The speech corpus had 25 words. On each trial one of the words was randomly chosen from the list, with replacement. Thus, on any given trial the stimulus was unpredictable, thereby reducing the availability of reliable spectral cues that might be used in the computation of sound source location. Stimuli were balanced for loudness using equal root-mean-square levels for all words. Stimuli were amplified and sent to the loudspeakers via Tucker Davis Technologies System III hardware. Stimulus levels averaged 60 dB SPL, with a random variation between 56 and 64 dB SPL (±4 dB) from trial to trial to minimize the availability of overall level cues.

Analyses of localization sensitivity employed a statistical non-parametric Kruskal-Wallis test to examine the relative independence of responses to each stimulus location, given a single response to an unknown stimulus. For each pair of locations in the loudspeaker array, the two response groups were analyzed using pairwise localization sensitivity index (LSI) values based on the z-scores from the p-value obtained bythe non-parametric Kruskal-Wallis test. The analysis produces a matrix of LSIs in coordinates of response locations. For N=15 target locations, the total number of LSI values was 105 [15*(15-1)/2=105]. The matrix is symmetrical about the diagonal. The matrixwas interpolated via the MATLAB contour function to find a contour of LSI with a z score of 1.65 (the 95th confidence level as the statistical threshold indicative of two locations being perceptually differentiated). We defined the contour of LSI = 1.65 as the sensitivity threshold. The overall localization sensitivity (LS) was characterized for individuals by averaging LSIs in the LSI matrix.

AbstractLocalizing sounds in our environment is one of the fundamental perceptual abilities that enable humans to communicate, and to remain safe. Because the acoustic cues necessary for computing source locations consist of differences between the two ears in signal intensity and arrival time, sound localization is fairly poor when a single ear is available. In adults who become deaf and are fitted with cochlear implants (CIs) sound localization is known to improve when bilateral CIs (BiCIs) are used compared to when a single CI is used. The aim of the present study was to investigate the emergence of spatial hearing sensitivity in children who use BiCIs, with a particular focus on the development of behavioral localization patterns when stimuli are presented in free-field horizontal acoustic space. A new analysis was implemented to quantify patterns observed in children for mapping acoustic space to a spatially relevant perceptual representation. Children with normal hearing were found to distribute their responses in a manner that demonstrated high spatial sensitivity. In contrast, children with BiCIs tended to classify sound source locations to the left and right; with increased bilateral hearing experience, they developed a perceptual map of space that was better aligned with the acoustic space. The results indicate experience-dependent refinement of spatial hearing skills in children with CIs. Localization strategies appear to undergo transitions from sound source categorization strategies to more fine-grained location identification strategies. This may provide evidence for neural plasticity, with implications for training of spatial hearing ability in CI users.